Crucial police files about missing Tauranga woman Luana Williams were destroyed during the investigation into her homicide - a move described by a high-profile investigator as either incompetent or sinister.
Documentary maker Bryan Bruce, whose programme The Investigator screens on TV One, was "appalled" to learn of the disappearance of the files.
Luana Williams disappeared from her Gate Pa home on June 5, 1986. Initial investigations led police to label it a suicide or missing person's case. The case has remained unsolved since it was re-opened as a homicide inquiry in 1994.
As part of his research into Miss Williams' disappearance, Mr Bruce said he applied under the Official Information Act for the release of Ms Williams' drug files.
She had been convicted for selling cannabis in 1983 as part of a police operation code-named "Kiwifruit", and Mr Bruce was keen to assess whether her murder could have been drug related.
In reply to his inquiry, Mr Bruce received a reply from Detective Inspector Paul Berry, who said the files were destroyed "somewhere around 1988 or 1989 in accordance with police instructions" but did not know who had issued that order.
Mr Bruce believes the files were stored in either Tauranga or Rotorua, and they could have contained useful information about Miss Williams' drug associates.
"Everybody must have known about the Luana Williams case, it was the talk of the town," Mr Bruce told the Bay of Plenty Times today.
"Everybody who had anything to do with the police at that time must have know that the Luana Williams case was a homicide.
"It seems to me this was either an act of incompetence or a sinister action by someone in the police who did not want whatever information was in those files to be seen."
Mr Bruce said the former detective who ran Operation Kiwifruit, Bob Bevege, had been surprised to learn Miss Williams' drug files had been destroyed.
"The destruction of files on a murder victim during the course of a homicide inquiry should be a matter of the gravest concern to any law enforcement agency concerned about maintaining its integrity," Mr Bruce said.
In the course of his investigation, Mr Bruce also learned that police were treating Miss Williams' death as a homicide as early as three months after her disappearance - yet the public were told it was still a missing person case.
"In a search document which I show [on the programme], it says 'this search is to be treated as a homicide but the public are not to know'.
"I ask the question, why not? Because people may have come forward for a homicide who do not come forward if it's listed publicly as a missing person. They may have thought Luana wanted to get out of the scene.
"Maybe their conscience would have told them to tell police something they know."
Mr Bruce hoped Wednesday's programme, which he said had the support of Miss Williams' family, might help solve the case.
"People are starting to talk now. Twenty-five years on, things change," he said.
"People who were frightened then may not be frightened now. Some people may have had religious experiences and changed their lives and feel they want to get something off their chest.
"There are people in Tauranga who know what happened to Luana, I'm absolutely convinced."
He urged anyone who knows anything about the case to come forward "so her family can get some peace".
Mr Bruce said anyone with information was welcome to contact him directly if they did not want to contact police.
In response to Bay of Plenty Times queries about the documentary, Western Bay of Plenty Police area commander Inspector Mike Clement said: "Luana Williams' disappearance remains unexplained and all options have been considered, including homicide.
"The investigation remains active and we would welcome contact from anyone who knows anything about Ms Williams disappearance."
The case has previously been the subject of a Sensing Murder investigation in 2006. Police received no fresh leads from the psychics.
Speaking to the Bay of Plenty Times in March last year, Detective Sergeant Eddie Lyttle said snippets of information on the case continued to come through.
There was no evidence to continue pressing people of interest in the case until further information linking them to Miss Williams' disappearance came to light, he said.
Top image: Flowers left at the site identified by psychics as the possible resting place of Luana Williams. Photo by Mark McKeown / File.
Bottom image: Bryan Bruce of TV show The Investigator / Photo: Supplied.